To date, amplifiers have been used in various electronic devices. It is generally known that efficiency of an amplifier is highest at an output saturated state (that is to say, a nonlinear state).
To date, proposals have been made of an outphasing amplification apparatus (hereinafter, sometimes referred to as an “outphasing amplifier”) as an amplification apparatus that causes an amplifier to operate in a saturated state. An outphasing amplifier includes two amplifiers connected in parallel, and a combiner for combining signals output from the two amplifiers, respectively. And a Chireix combiner is used as the combiner. The Chireix combiner has a λ/4 transmission line on a first line connecting a first amplifier and a combination point, and a λ/4 transmission line on a second line connecting a second amplifier and the combination point. Here, if the combined phase is not in phase, load impedance of the first amplifier has a reactance component that is the same size, but the opposite polarity as the reactance component of the load impedance of the second amplifier. Thus, in order to compensate those reactance components, the Chireix combiner is provided with a shunt reactance.
Related-art techniques have been disclosed in Japanese Laid-open Patent Publication Nos. 2009-213090, 2007-174148, and 2006-314087, and Japanese National Publication of International Patent Application No. 2009-533947.
Incidentally, improvements in power efficiency characteristic and broadband characteristic are demanded for amplification apparatuses. if a circuit size becomes large, these characteristics are deteriorated.
On the contrary, it is possible to improve these characteristics by reducing the circuit size. Accordingly, it is demanded that the circuit size of an amplification apparatus is made small as much as possible.